Question

I am trying to run the following code but it gives me garbage data on accessing the struct array values. Why is this happening and how can I fix this? Once I move the malloc part to the main function it seems to work. But I want to keep the malloc in a separate function.

#include <cstdlib>
#include <limits>
#include <iostream>
using namespace std;

/*
 *
 */
typedef struct{
    float x;
    float y;
} CoordinateData;

void tester(CoordinateData* cd_data){
    cd_data = (CoordinateData*)malloc(5*sizeof(CoordinateData));
    CoordinateData data = {41.2525,74.0744};
    *cd_data = data;

}
int main(int argc, char** argv) {

    CoordinateData* cd_data;
    tester(cd_data);
    std::cout << (*cd_data).x << "::" << (*cd_data).y << std::endl;
}

The output I get is 2.42126e-39::-1.51015e-05
The expected output is 41.2525::74.0744

Answer 1

Pass cd_data by address, not value:

void tester(CoordinateData** cd_data)
{
    *cd_data = (CoordinateData*)malloc(5*sizeof(CoordinateData));
    CoordinateData data = {41.2525,74.0744};
    *(*cd_data) = data;
}

int main(int argc, char** argv)
{
    CoordinateData* cd_data = NULL;
    tester(&cd_data);
    std::cout << (*cd_data).x << "::" << (*cd_data).y << std::endl;
    free(cd_data);
    return EXIT_SUCCESS
}

Note also, the return value of main() which you were missing. Also. this question is tagged as both C and C++. If it is the latter, use new and delete[] instead of malloc and free